Cambridge University is warning ministers that it will be forced to admit fewer state school students if a shakeup of A-levels goes ahead, it emerged today.

The university's head of admissions, Geoff Parks, has written to the education secretary, Michael Gove, to say it would be wrong to change A-level exams so that students sat them only after two years of study. Gove said this month he would implement reforms over the next three to five years to end A-levels being broken up into "bite-sized" AS-levels that can be taken throughout the course. He said they failed to prepare students for the demands of a degree and scrapping them would signal "the revival of the art of deep thought".

Parks's letter, sent to the Times Educational Supplement, said AS-levels were an "invaluable indicator of progress" that had helped the university increase its intake of students from low-income families in state schools.

Figures from 2007-8 show that the number of state school pupils at Cambridge rose to 59%, compared with 55% the year before.

Parks wrote: "A large part of this success derives from the confidence engendered in students from non-traditional backgrounds when they achieve high examination grades at the end of year 12. We are worried ... that if AS-level disappears, we will lose many of the gains in terms of fair admissions and widening participation that we have made in the last decade."

The Department for Education said it was clear that confidence in public exams needed to be restored. "We are listening carefully to universities, employers and academic subject bodies' views to ensure A-levels are rigorous and equip young people for higher education," said a spokesman. "We will look in detail at exam structure, including whether schools and colleges should be able to offer traditional two-year A-levels alongside or instead of modular A-levels."